Update LLVM from 18 to 22

[stertl]

Changes

Bumps the LLVM version from LLVM 18 (llvmorg-18.1.8) to LLVM 22 (llvmorg-22.1.6). The ARC architecture target branch is updated accordingly from release/18.x to release/22.x.

Motivation

LLVM 22 delivers a significant AoT compilation speedup compared to LLVM 18. Compiling an example program (example.c.zip — a large C file with many global variables) to AOT shows:

wamrc version	Wall time
wamrc 2.4.4 (LLVM 18)	66.79 s
wamrc with LLVM 22	12.59 s

~5× speedup — the updated compiler takes roughly one fifth of the time of the previous version for this workload.

Testing

# Compile C to Wasm
$ time clang-21 -target wasm32 -O3 -nostdlib example.c -Wl,--no-entry,--export=function -o example.wasm

# Compile Wasm to AoT with wamrc-2.4.4 with LLVM 18
$ time wamrc-2.4.4 -o example.aot example.wasm                                                                    
Create AoT compiler with:
  target:        x86_64
  target cpu:    skylake
  target triple: x86_64-unknown-linux-gnu
  cpu features:  
  opt level:     3
  size level:    3
  output format: AoT file
Compile success, file example.aot was generated.
wamrc -o example.aot example.wasm  66.79s user 0.04s system 99% cpu 1:06.83 total

# Compile Wasm to AoT with wamrc with LLVM22
$ time ./wamr-compiler/build/wamrc -o example.aot example.wasm
Create AoT compiler with:
  target:        x86_64
  target cpu:    skylake
  target triple: x86_64-unknown-linux-gnu
  cpu features:  
  opt level:     3
  size level:    3
  output format: AoT file
Compile success, file example.aot was generated.
/home/stefan/git/siemens-wasm-micro-runtime/wamr-compiler/build/wamrc -o    12.59s user 0.13s system 99% cpu 12.719 total